Electrical Troubleshooting Quiz — May 5, 2026

The plant has several large production machines. One of them seems to have a motor failure every few months. The response has always been to replace whichever motor has failed. There are three of them. Two of them are 10HP each, and the main drive motor is 75HP. The plant controller has complained about the cost, and the production superintendant has complained about missing shipment deadlines due to the downtime.

You don’t normally work in that area of the plant, but the maintenance manager has specifically assigned you to get to the bottom of this. He asked you where you would start. You told him that since this problem is local to that machine, it’s not a general power quality problem. But, you said you would start by looking at the local power quality. The shop has a portable power analyzer you can use to make short work of that. He agreed you should start there. You did, and you found no anomalies.

Where do you look now?

Answer to Quiz

Step back and look at the whole machine. What do you see? Are there boxes, crates of parts, or other things blocking air flow to the motors? How clean is the machine and the area around it? Excess dust or other particulates can block motor vents, plus insulate the motor casings so they hold in heat.

Since this problem is such a thorn to the plant controller and the plant manager, they should not object to paying for a forensic evaluation of any of the motors that have failed. If those are now gone, get authorization now to send the next failed motor to a motor repair shop for a post-mortem. A good shop can nearly always tell you what the failure mode was and also point out contributing factors. For example, they can not only tell you if the motor died from bearing failure but they can read the bearings to tell you what most likely caused that particular failure.

A common cause of bearing failure is incompatible greases used to lubricate the motor. Not far behind that is improper lubrication procedure (not cleaning the zirc before adding grease, not removing the drain plug, etc.).

Note that under greasing leads to overheated bearing, while over greasing usually causes overheated bearings plus problems with the windings. Many people don’t understand this, so here’s the explanation. Grease is a combination of oil and a substrate. Over greasing causes friction between the excess substrate and the metal, increasing the temperature to the point where the substrate melts and the grease runs out. Now you have an under greased bearing, but you also have oil getting into the windings.

Find out who has been lubricating motors on this machine, what greases that person has been using, and how he has been doing the lubrication procedure. In some plants, that is the operator’s job (which it should not be).

This machine may have suffered a collision with a lift truck. If a lift truck operator accidentally backed into a motor pedestal with those heavy counterweights, the motor base and/or pedestal may be twisted, cracked, or damaged in some other way. This would cause vibration, which could easily be transmitted between the motors. So check each motor with a vibration analyzer to rule out this and other issues such as overtightened mounting bolts. If there is a vibration problem, solve for the cause and then install vibration sensors to permit remote automatic vibration measurement.

All of this assumes the motors are the correct ones for the application. But what if they are not? Then even if you do solve the preceding problems, you will still have premature motor failure. Start by checking the motor nameplate to see the NEMA or IEC designation. Then look that up to see if the motor is correct for the type of load. For example, if those motors are NEMA Class B but the machine has high inertia loads you have the wrong type of motor. You will need to change those out for NEMA Class C.

Also consider the heat rating of the motor, if operation of the machine exposes any of those motors to high heat. For example, a motor with Class A insulation is good for about 105 degrees F. You could step to Insulation Class B with each replacement, and in the meantime see if you can reduce the temperature around the motor through such measures as adding thermal insulation between the motor and the heat source, and/or adding ducts and forced ventilation. One plant in northeast Georgia hired a local contractor to custom-build a sheet metal shroud and then added an enclosure cooler to the inside of the shroud.

If the motor already has some kind of cooling or ducting system, check to see if that system has air filters. If it does and these are cumbersome to change, have a sheet metal contractor replace the filter mount with a simple vent that is 10x10. Affix a screen mesh over the vent, glue four strips of hook and loop fastener around the vent, then order a box of precut 12x12 filter media. A filter change that used to take fifteen minutes now takes three seconds (actual times from a plant in Kentucky that did this very thing).

If this machine still has excess failure rates, it’s almost certainly something the operator is doing. A small shop in Loves Park, Ill. had eight machines that were identical, except they were set up for different product runs and had different operators. One machine had a breakdown a couple of times per week. The other machines almost never broke down. Finally, the production manager had the operator of that machine trade with the operator of another machine that hadn’t broken down in over a year. After three weeks, the “problem machine” had not broken down once, but the “reliable machine” broke down several times. Having a “blame the operator” discussion is tricky, at best. You can often avoid that by asking the production manager to change operators for a few weeks to see what happens.